Field of the Invention
The present invention particularly relates to an image processing system to be suitably used to reduce a difference of color of same subjects in images, an image processing method for the image processing system, a program for performing the image processing method, and a recording medium for storing the program.
Description of the Related Art
Conventionally, there has been a system in which plural cameras are installed in a convenience store, a shopping mall, an airport or the like, and the installed cameras are connected to a PC (personal computer) or the like via a network to be able to watch or monitor plural points. For example, the system concerned is used to search for, from among plural video images photographed or shot by currently used cameras, a specific person such as a shoplifter or the like included in a recorded video image past photographed or shot by a certain camera. At this time, it is possible, by arranging and displaying both the recorded video images and the video images of the plural cameras currently used and then visually confirming these images, to know or grasp which photographing range of the camera/cameras the specific person is currently in.
In case of visually identifying the specific person from among the video images of the plural cameras, it is difficult to correctly identify the specific person if the color of the specific person has been shifted or deviated. Here, it has been known that the color reproduced on the camera is influenced according to the color temperatures of environmental light at the place where the relevant camera has been installed. For example, when an object illuminated by a fluorescent lamp and an object illuminated by an incandescent lamp are compared with each other, the blue portion of the object is strongly reproduced under the fluorescent lamp, whereas the red portion thereof is strongly reproduced under the incandescent lamp. At the outdoors in fine weather, the color temperature at a sunny place is different from that at a shaded place. Since the cameras are installed under various illumination conditions, the installed camera is greatly influenced by the above difference of the color temperature of the environmental light. Besides, the color reproduction characteristic of the camera differs if an optical system such as a lens, an image pickup element, or the like differs. Thus, when the plural cameras are installed, it is difficult to prepare and provide all the cameras having the same color reproduction characteristic. As a result, the color reproduction characteristic is different for each camera.
As just described, such a watch camera (security camera) network has an inevitable problem that a difference of color occurs between the cameras. For this reason, the technique of correcting this difference of color between the cameras has been proposed.
Japanese Patent Application Laid-Open No. 2007-329555 discloses the method of correcting the colors between the plural cameras arranged such that the parts of the adjacent photographing areas overlap each other. In this method, the color histogram (i.e., the integrated value of RGB signals) is calculated for each color by using the overlapped photographing areas, and adjusted to reduce the difference between the calculated integrated values of the camera images for each color.
However, in the above related art, a problem occurs when it intends to watch the wider area. Namely, it typically becomes difficult to arrange the cameras such that their photographing areas always overlap each other, in proportion as the place to be watched becomes wider. Therefore, the photographing areas of the plural cameras do not often overlap each other, and it is impossible in such a case to reduce the difference of color. Thus, it is impossible by the method disclosed in Japanese Patent Application Laid-Open No. 2007-329555 to correct the difference of color.
Therefore, in the above related art, when the photographing areas of the cameras do not overlap each other, it is necessary for a user to instruct the camera, for which the color correction is performed, to photograph a reference chart and/or to designate the target person images as the same person image. Consequently, a heavy load is applied to the user.
Accordingly, the present invention aims to provide the technique capable of reducing the difference of color between the plural cameras even in the case where the photographing ranges of the plural cameras do not overlap.